She is _NOT_ locked out, and can send to internal emails, and to most other places she can email just fine, and usually if I try a couple times it'll work or sometimes we just wait and it starts working again, any ideas?

We had a user get that same error message and found out that instead of clicking on the email link in the signature of the message, he was copying and pasting the link into the "to:" field. If most of her email goes out correctly, I would see what is different about the effected addresses.

I'm glad you fixed your issue. My problem was also caused by Symantec PGP but I was able to fix it by modifying my network firewall.

Previously iptables had been reloading its rules every hour (I was still setting it up and didn't want to lock myself out). The emails that failed to go out were always timestamped a few minutes after the hour. I switched iptables to reload every night at midnight and the issue went away.